In the past, 4 resins, phenol-formaldehyde, melamine-formaldehyde, isocyanate and urea-formaldehyde resins, have been most commonly used for commercially produced interior and exterior particle boards. Of these resins, phenol formaldehyde resins have become the standard by which all resins are measured, chiefly because they are relatively inexpensive, and have sufficient hydrolytic resistance for exterior applications. However, phenolic resins have a relatively slow cure rate and usually require resin in excess of that normally necessary to be used to overcome the swelling tendencies of cellulose materials when exposed to moisture and caustic. Phenolic resins are insensitive to overcure, and do not stick to molding apparatus. A second, though less popular resin, melamine-formaldehyde, is generally comparable to phenolic resins, however, is more expensive. The third commercially popular resin in use are the polymeric isocyanates, as discussed in the report, "The 11th Particleboard Proceedings," Washington State University, 1977. Isocyanate resins are as good if not better in water resistance properties as phenolic resins, and in addition are fast curing, though expensive. Primarily because isocyanate resins can be used at approximately one-half the rate of application of phenolic resins to achieve the same strength board, while at the same time using less wood, and because of their inherently faster rate of cure, the cost differential between isocyanates and phenolic resins is becoming smaller. Boards bonded with an isocyanate resin, when compared to phenolic resins of the same strength, are lighter and therefore easier to handle at a job site. Being lighter, they are less expensive to ship and thus are a preferred product. The remaining resin, urea-formaldehyde is appropriate for use in interior boards only, as a result of its inherent instability in the presence of moisture.